Samoans are one of the few populations to use citrus leaves, or laumoli, in the kitchen. I mean, lots of people drink tea made from lemon leaves, but not many use the leaves to actually cook with. The Thai people famously use kaffir lime leaves in their curries and the Vietnamese fry lemon leaves up with grubs. And a few Mediterranean populations use citrus leaves for wrapping food and in marinades.
What we do use orange or lemon leaves for is very simple - to impart a subtle citrus fragrance to sweet dishes such as koko araisa (cocoa rice) and sua araisa (milky rice).
Take your orange or lemon leaf from a tree that hasn't been treated with chemicals. You want to choose leaves that are dark green, not the young lighter coloured ones, because the darker, more mature leaves have got more citrus oils (e.g. flavour) in them. Throw your leaf in the simmering dish, but like a bay leaf, it's not to be eaten. The leaf will leave a hint of orange or lemon flavour, but the dish won't be overwhelmed by it.
If you can't get your hands on fresh citrus leaves, then try substituting with the fruit zest or essence. But citrus leaves are never an essential ingredient, so you can always leave them out.